Data Centre Cooling System

ABSTRACT

A method of cooling a data centre, and a data centre, is disclosed. Optionally, the data centre comprises: a cooling air source (201); at least one rack room (202) having a floor and rack storage areas (203a-203d) on the floor, each rack storage area accommodating racks in which items of electronic equipment having at least one fan (204) are housed; one or more cold aisles (205) in the rack room, each cold aisle being adjacent to a rack storage area; one or more hot aisles (206) in the rack room, each hot aisle being adjacent to a rack storage area; and an air supply corridor (207) for transporting cooling air, above the floor, from the cooling air source to the one or more cold aisles. The method optionally comprises transporting cooling air from the cooling air source (201) to the one or more cold aisles (205) substantially under the control of the fans (204) of the items of electronic equipment.

FIELD OF THE INVENTION

The present invention concerns data centres and a method of coolingequipment in a data centre. The invention also concerns apparatus forcooling a data centre.

BACKGROUND OF THE INVENTION

A data centre is a late 20th Century development that has grown as aresponse to the increasing demand for computer processing capability anda recognition of the importance of information technology (IT) in theplace of every business and organisation today. Whereas smallerorganisations have sufficient processing power with laptops, PCs andoccasionally servers, larger organisations require higher capacitycentralised processing to serve a wide range of needs and applications.A few years ago this capacity was supplied by large mainframe computers,but more recently the method used has been to provide data centrescomprising many networked computer servers known as “blades” installedin racks enabling controlled and modular expansion of capacity. Theracks also typically house storage systems and/or telecommunicationsequipment such as routers to handle data flow between the computerservers and data flow between the data centre and the outside world.

One key problem faced is how to cool a data centre effectively andefficiently. It will be appreciated that data centre facilities are ofcritical importance to their users, and so overheating of servers (whichis likely to cause the server to temporarily or even permanently fail)must be avoided.

One method of the prior art, now recognised to be inefficient, is toprovide a room in which air-conditioning units (mechanical DX coolers)flood the room with chilled air (by drawing air from the room, chillingit, and then pumping the chilled air so produced back into the room) soas to provide a reservoir of chilled air from which the servers may drawcooling air by means of their internal fans. No entrainment of coolingair is provided.

In another data centre arrangement of the prior art, the racks are laidout in rows. Cooling is provided by direct expansion (DX) or chilledwater cooling plants. The cool air produced by these units is entrainedthrough an underfloor plenum and exits through floor grilles at thefront of the IT rack rows. The IT products installed in the rackscontain integral fans which draw the cooled air from the front acrossthe circuitry and heat is exhausted via vents in the products to therear.

A typical version of the prior art arrangement utilising under-floorcooling and racks in rows, is shown schematically in FIG. 1 of theattached drawings. Thus, the data centre includes a rack room 1 definedby walls 2 in which two sets of racks 4 for IT equipment areaccommodated. The IT equipment in the racks 4 generate heat, representedby arrows 6. The cooling of the IT equipment is achieved by introducingcold air, via a floor void, into the room by means of air conditioningunits, the cold air being represented by arrows 8.

The drive for more efficient use of power has given rise to a need tomake the cooling regimes used in data centres more efficient, as coolingof equipment typically contributes significantly to the power used by adata centre. For example, the power usage in certain data centres mayrequire between 1 kW and 2 kW of power for every 1 kW of power used topower the IT equipment, a significant proportion of which would berelated to cooling.

In certain arrangements of the prior art, the separation between ITracks creates a ‘hot aisle’ into which air is expelled by the ITproducts in the racks and a ‘cold aisle’ from which cooler air is drawninto and through the IT products by their integral fans. In sucharrangements, it is important to maintain a controlled air flow so thatno ‘hot spots’ are created within the rack room where overheatingservers are not in fluid communication with cooling air. One method ofavoiding this problem is to supply significantly more cold air than theservers actually need at any given time and ensuring that the requiredamount of cooling air is provided to every server in the rack room.

Typically, cooling air is transported from the cooling plant to theracks via duct work and/or an underfloor plenum, both of which addsignificant resistance to air flow. In order to supply the large volumesof cooling air required to ensure that each and every server is suppliedwith an adequate amount of cooling air, the cooling air has to travel athigh velocity through the duct work and/or the underfloor plenum.Typically, large, powerful fans are used to drive the cooling air fromthe cooling plant to the servers. When air is supplied to a cold aislevia duct work and/or an underfloor plenum at high velocity, it can bedifficult to ensure that each and every server in the cold aisle iseffectively cooled. For example, servers located close to the point atwhich high velocity cooling air enters the cold aisle are often bypassedby the cooling air stream because the integral server fans are notpowerful enough to redirect the cooling air and draw the air across theserver effectively. One approach to reducing the velocity of the coolingair (whilst maintaining adequate cooling) is to lower the temperature ofthe cooling air by increasing the amount of mechanical cooling. However,reducing the temperature of the cooling air is an energy intensiveprocess that reduces the efficiency of the data centre.

One approach to improving the efficiency of data centre cooling is toutilise ambient outside air in addition to or instead of mechanicallycooled air. Often, in data centre cooling methods utilising cooling aircomprising ambient air, the temperature of the cooling air is higherthan in cooling methods utilising cooling air consisting of mechanicallycooled air. Typically, to achieve adequate cooling using highertemperature cooling air, the airflow across the servers needs to behigher, and so even larger volumes of cooling air need to be supplied tothe cold aisles. WO2010/139919, WO2011/073668, WO2011/148175 andWO2010/139921 disclose methods of utilising ambient air from outside adata centre to cool items of electronic equipment in which cooling airis transported to the cold aisles via an access corridor, thus providinga relatively low resistance path via which large volumes of cooling aircan be transported to the cold aisles at low velocity. To ensure thatthe servers are provided with an adequate amount of cooling air, thosemethods utilise large fans upstream of the servers to maintain apositive pressure of cooling air in the cold aisles relative to thepressure of the hot air in the hot aisles.

In general, known methods of cooling data centre buildings having acontrolled air supply path with hot and cold aisle separation, themethods comprising the use of ambient air (optionally with filtration ofthe air), mechanically cooled air (for example using direct expansion orchilled water cooling plants), and/or humidification/dehumidification ofcooling air, utilise banks of fans, individual large fans, and/orcooling equipment comprising large integral fans.

Although considered necessary to ensure adequate and reliable cooling,the operation of large central fan arrangements accounts for asignificant proportion of a data centre's energy usage. Furthermore,such central fan arrangements can become a single point of failure forthe data centre. For example, should a fault develop with a central fanarrangement, the entire data centre might be forced offline.Additionally, during operation, large fan banks produce undesirablelevels of noise. Often, sound attenuation equipment is used to reducethe volume of the fan noise transmitted to other parts of the datacentre, for example personnel corridors and server rooms, and itssurroundings. Such sound attenuation equipment adds to the constructionand maintenance cost of the data centre, and adds resistance to the airflow path in turn necessitating the use of stronger fans and leading toan increase in operational costs.

A small number of methods use convection to draw cooling air through adata centre building as an alternative to using central banks of fans.In such methods, hot air rises through high level chimneys and or roofridge vents, with assistance from the prevailing wind to draw air out ofthe top of the building and to push ambient air into a lower part of thebuilding through external wall vents. A drawback of such designs is thatthey require careful planning and siting since their utility isdependent on finding an appropriate location. The limited number ofsuitable locations and the requirement to design each new data centreindividually significantly reduces the flexibility of such methods.

The present invention seeks to provide an improved method and apparatusfor cooling a data centre. Alternatively or additionally, the presentinvention seeks to provide a system for cooling a data centre thatmitigates one or more of the above mentioned disadvantages.

SUMMARY OF THE INVENTION

The present invention provides, according to a first aspect, a method ofcooling a data centre having one or more racks of items of electronicequipment (for example operational IT equipment such as rack-mountedservers, rack-mounted network equipment or the like) each having its owncooling fan, and preferably one or more associated cold aisles, in whichmethod cooling air is transported, substantially under the control ofthe fans of the electronic equipment, from a cooling air source to theone or more racks of items of electronic equipment, preferably via oneor more cold aisles. The data centre preferably comprises the coolingair source. There may be at least one rack room having a floor and aplurality of rack storage areas on the floor, each rack storage areaaccommodating a plurality of the racks in which a plurality ofrack-mountable items of electronic equipment, each having at least onefan, are housed. Each cold aisle is typically adjacent to a rack storagearea. There may be one or more hot aisles in the rack room. Each hotaisle will typically be adjacent to a rack storage area. There may be anair supply corridor for transporting cooling air, above the floor, fromthe cooling air source to the one or more cold aisles.

It will be appreciated that, because cooling air is transported from thecooling air source to the one or more cold aisles substantially underthe control of the fans of the rack-mountable items of electronicequipment, either the cooling air source has no fans (or is not directlyassociated with any fans), or the cooling air source has one or morefans that play no significant part in supplying cooling air to the itemsof electronic equipment.

It may be that the method allows a data centre to be ‘scaled up’ moreeasily, for example because adding additional items of IT equipment eachhaving one or more integral fans to a data centre cooled according tothe method also adds air moving capability to the data centre. In knownmethods that, for example, use large, fixed banks of fans in a coolingair source to control the transport of cooling air from the cooling airsource to the items of electronic equipment, the capacity of the methodto move cooling air, and thus the number of items of electronicequipment that can be cooled, is fixed at the time of construction ofthe data centre. It will be appreciated that such known methods ofcooling items of electronic equipment may limit subsequent expansion ofthe data centre. Thus, it may be that the present method provides a moreflexible method of cooling items of electronic equipment.

It will be appreciated that the rack storage areas may comprise serverracks, also known as ‘blade’ racks, server cabinets and ‘blade cabinets.It may be that the rack storage areas are arranged in rows, for examplea row of server racks or cabinets arranged in a continuous line.

A data centre building comprising segregated hot and cold aisles and anair supply corridor for transporting cooling air from the cooling airsource to the one or more cold aisles provides a low resistance, highvolume air flow path through the data centre and prevents unwantedmixing of cold and hot air. Embodiments of the method of the firstaspect of the invention may utilise a data centre building having anarchitecture and internal layout creating very low/minimal airresistance with substantially (or entirely) all entrainment of airthrough large open areas. It will be appreciated that it is desirable inoperating the method of the present invention to make efficient useof/optimise the layout and internal dimensions of the data centre inorder to minimise the resistance to air flow around the building (or atleast to create an air flow path having a resistance that issufficiently low to facilitate practical operation of the method of theinvention). Such a low resistance, high volume air path environmentreduces the requirement for mechanical air circulation, thereby allowingthe fans of the items of electronic equipment to move air around thedata centre through their own fan power. A large cold space (comprisingthe one or more cold aisles and the air supply corridor) may provide areservoir of large volumes of treated cooling air having the temperatureand humidity required to effect efficient cooling. It will be understoodthat “treated air” is air having a temperature and a humidity fallingwithin pre-determined upper and lower temperature and humidity limits.It may be that a large reservoir of readily available cooling air isuseful in modes of operation of the data centre in which coolingrequirements fluctuate rapidly due to increases and decreases in load onthe items of electronic equipment.

There may be a well-defined airflow path along which air flows withinthe data centre to and from a given item of electronic equipment in arack. Such a path may for example be deemed to start at the cooling airsource, then follow the air supply corridor above the floor, then enterthe cold aisle associated with the rack in which the given item ofelectronic equipment is accommodated, then pass from one side of therack to the other, for example via the space occupied by the given itemof electronic equipment and thus through the fan of the item ofelectronic equipment, and then into a hot-air extraction path, forexample along a hot aisle and possibly subsequently a hot air corridoror air extraction corridor. The flow paths of air for cooling the itemsof electronic equipment in the racks may be such that they allow for theair flows to cooperate and combine together. It may be that the buildingand infrastructure (ducts, corridors, aisles for example) that providethe space within which the air may flow dictates the direction of theair flow path(s). Thus, air flows in the data centre may be entrained sothat air flowing to a given item of electronic equipment is encouragedto flow along a predetermined path. It may for example be that thestructure above and below, and to either side of an air-flow path,guides the air along its flow path with the assistance of the flowcaused by the fans in the electronic equipment. This may, for example,be viewed in contrast with the case in which servers are provided in anopen room flooded with air-conditioned air in which there is noentrainment of air.

Preferably, the cooling air flow path leading from the cooling airsource to the rack-mountable items of electronic equipment has a sumvolume that is at least 75%, for example at least 90%, of the volume ofthe warm air flow path leading from the rack-mountable items ofelectronic equipment back to the cooling air source. Optionally, thecooling air flow path leading from the cooling air source to therack-mountable items of electronic equipment has a sum volume that isfrom 75% to 125%, for example from 90% to 110%, of the volume of thewarm air flow path leading from the rack-mountable items of electronicequipment back to the cooling air source. It will be appreciated thatwhen the data centre comprises an air supply corridor and one or morecold aisles, the sum volume of the cooling air flow path comprises thetotal air volume of the air supply corridor and the total air volume ofthe one or more cold aisles. For example, if the data centre comprises acooling air source that supplies air directly into an air supplycorridor having a cross-sectional area of 6 m² and a length of 20 m, andfive cold aisles having a cross-sectional area of 5 m² and lengths of 10m, the cold aisles being directly connected to the air supply corridor,the sum volume of the cooling air flow path would be 370 m³. If thatdata centre comprises five hot aisles directly connected to an airexhaust corridor for returning warm air directly back to the cooling airsource, the sum volume of the hot aisles and the air exhaust corridor isoptionally from 278 to 463 m³, preferably 333 to 407 m³. It may be thatwhen the sum volume of the cooling air supply path is similar to orlarger than the sum volume of the warm air return path, an imbalance inresistance to air flow that might otherwise exist is reduced in the datacentre. It may be that having a sum volume of the cooling air supplypath that is similar to the sum volume of the warm air return path isparticularly useful when the cooling air source is an indirect airhandling unit. It may for example be that the difference in the sumvolume of the cooling air supply path and the sum volume of the warm airreturn path is less than 50% of the larger volume, preferably less than20% difference.

It may be that the data centre does not include a sound attenuationdevice along the air flow path from the cooling air source to the racksof items of electronic equipment. The absence of a sound attenuationdevice along the airflow path may further reduce resistance to air flow,thus improving the efficiency of the method.

It may be that the air flow path from the cooling air source to racks ofthe items of electronic equipment does not include duct work (ductinghaving a cross-sectional area of 2 m² or less) or an underfloor plenum.Optionally, the air flow path from the cooling air source to the racksof items of electronic equipment does not include an over-ceilingplenum. Preferably, the air flow path from the cooling air source to theracks of items of electronic equipment consists of the air supplycorridor and the cold aisle.

When the transport of cooling air from the cooling air source to the oneor more cold aisles is substantially under the control of the fans ofthe rack-mountable items of electronic equipment, the efficiency of themethod of cooling the data centre building is improved because there islittle or no duplication in operation of equipment to transport thecooling air from the cooling air source to the racks of items ofelectronic equipment. Furthermore, the failure of one or more fans on aparticular item of electronic equipment does not reduce the cooling ofother items of electronic equipment which each comprise their own fan orfans. Thus, it may be that the method of the first aspect of theinvention allows for the temperature and/or humidity of the cooling airto be maintained through a control system (the cooling air source),providing the flexibility of a full mechanical fan-driven system butwithout the associated costs (both of construction and operation),complexity and redundancy drawbacks and risks.

Preferably, the method of cooling items of electronic equipmentcomprises transporting the cooling air from the cooling air source tothe one or more cold aisles entirely under the control of the fans ofthe rack-mountable items of electronic equipment. When the transport ofcooling air is controlled entirely by the fans of the electronicequipment the efficiency of the method is further improved because itallows for further reduction in duplication and redundancy, that mightotherwise be required/present in the method.

Optionally, the air supply corridor of the data centre building has across-sectional area of at least 3 m², preferably at least 5 m², forexample at least 9 m², along 90% of its length. It has been found thatwhen the air supply corridor has a cross-sectional area of 3 m² or morealong 90% of its length the resistance to air flow around the datacentre building is reduced, thereby reducing the air velocity requiredto transport a given volume of cooling air from the cooling air sourceto the cold aisles, thus also reducing the demand placed on the fans ofthe items of electronic equipment. Preferably, the air supply corridorhas a cross-sectional area of at least 3 m², such as 5 m², for example 9m², for its entire length from the cooling air source to the one or morecold aisles.

Preferably, the cooling air source is arranged such that cooling airexiting the cooling air source flows directly into a personnel area inthe data centre. Optionally, the cooling air source is in the form of anair treatment unit, wherein the air treatment unit is arranged in thedata centre so that cooling air exiting the air treatment unit flowsdirectly into a personnel area of the data centre, for example withoutpassing through any ductwork. Preferably, the data centre comprises acooling air flow path leading from an air treatment unit cooling airsource to one or more cold aisles, wherein that cooling air flow path issubstantially, optionally entirely, free from ducting. Preferably, thedata centre comprises a cooling air flow path leading from an airtreatment unit cooling air source to one or more cold aisles that isaccessible to personnel along at least 90% of its length. It will beappreciated that an air flow path that is accessible to personnel issized and configured such that personnel can enter and pass along theair flow path (the path, for example being designed for an average adultto be able to walk in). As used herein, a ‘personnel area’ is an area ofthe data centre designed to be readily accessed by personnel andoccupied by at least one adult in a standing position, for example beingin the form of a corridor, a room, or the like. It will be appreciatedthat data centre personnel areas may only infrequently be occupied oraccessed by personnel. The inside of an air-duct having a cross-sectionof less than 0.5 m² would not be considered as being a personnel area.

Preferably, at least part of the air supply corridor is located on thesame level of the data centre as one or more cold aisles. Optionally, atleast part of the air supply corridor is located on the same floor ofthe data centre as the one or more cold aisles.

Preferably, the air supply corridor provides personnel access to atleast one cold aisle. Additionally or alternatively, the air supplycorridor may provide personnel access to at least part of the coolingair source.

Preferably, the air supply corridor has a height of at least 1.5 m, suchas at least 2 m, above the floor for at least 90% of its length.

Preferably, the cooling air source comprises an adiabatic humidifier,and the method comprises controlling the adiabatic humidifier to adjustthe humidity and/or temperature of the cooling air. Preferably, themethod comprises operating the adiabatic humidifier to adjust thetemperature and/or humidity of the cooling air according topre-determined temperature and/or humidity ranges. It has been foundthat an adiabatic cooler can provide a particularly efficient means ofcontrolling the temperature and humidity of the cooling air. It will beappreciated that in order to efficiently and safely cool therack-mounted items of electronic equipment, the temperature and humidityif the cooling air should fall within desired temperature and humidityranges.

It may be that the cooling air source provides cooling air through theuse of an air conditioning arrangement that may, according to need,include evaporative cooling, DX cooling, filtration of ambient air,and/or control louvres to regulate air flow. It may be that the coolingair source is in fluid communication with the ambient air outside thedata centre building. Additionally or alternatively, it may be that thecooling air source is indirectly in contact with a cooling fluid (suchas the ambient air outside of the data centre building), for example bymeans of a heat exchanger.

Preferably, the cooling air source is a direct air handling unit thatsupplies cooling air comprising ambient air from outside the datacentre. Preferably, the direct air handling unit comprises one or moreadiabatic cooling units, such as a wetted matrix humidifier for coolingthe ambient air. Preferably, the direct air handling unit comprises oneor more filters for filtering the ambient air. Preferably, the one ormore filters are low-resistance filters. Preferably, the direct airhandling unit comprises one or more mechanical cooling units, such as aDX cooling unit.

Preferably, the cooling air source is an indirect air handling unithaving an external air flow path segregated from an internal air flowpath. Optionally, the indirect air handling unit comprises one or moreheat exchangers, for example comprising one or more heat tubes, forexchanging heat between air flowing along the internal air flow path andthe external air flow path. Preferably, the indirect air handling unitcomprises one or more adiabatic cooling units, such as a wetted matrixhumidifier, in the external air flow path. Preferably, the indirect airhandling unit comprises one or more mechanical cooling units, such as aDX cooling unit, in the internal air flow path. Preferably, the coldaisles of the data centre are in fluid communication with the internalair flow path of the indirect air handling unit. Preferably, theinternal air flow path of the indirect air handling unit issubstantially free, for example entirely free, from fans for pushingcooling air to the electronic equipment. Preferably, air is transportedalong the internal air flow path of the indirect air handling unitsubstantially, for example entirely, under the control of the fans ofthe rack-mountable items of electronic equipment. Preferably, theindirect air handling unit comprises a plurality of external air fansfor transporting ambient air from outside the data centre along theexternal air flow path. Preferably, when the cooling air source is anindirect air handling unit, substantially all of the cooling airtransported by the fans of the rack-mounted items of electronicequipment is ‘internal air’, that is, air that is recirculated aroundthe data centre. For example, when the cooling air source is an indirectair handling unit, air may flow around the data centre in a closed loop,such as a closed loop extending from the indirect air handling unit tothe electronic equipment and back to the indirect air handling unit. Itwill be appreciated that such a data centre may nevertheless compriseone or more systems for refreshing the internal air by admitting airfrom outside the data centre into the closed loop system. For example,the data centre may comprise an auxiliary air vent for admitting freshair into the data centre. In operation, the auxiliary air vent may beoperable to admit, for example, a volume of air equivalent to theinternal air volume in the data centre more often than once a day, butless often than once a minute (for example at a rate of the order ofonce every hour). It may be that such a system for refreshing the air isprovided to avoid the build-up of stale air inside the data centre.

Preferably, the cooling air source comprises an adjustable inlet ventfor admitting outside air into the data centre building, and the methodcomprises controlling the adjustable inlet vent to vary the amount ofoutside air admitted into the data centre building. It may be that whenthe method controls the amount of ambient air admitted into the buildingthrough the adjustable inlet vent the method efficiently balances thecooling air requirements of the electronic equipment to reduce (andpreferably substantially minimise) the amount of mechanical coolingand/or humidification/dehumidification required.

Preferably, air to be cooled is transported to the cooling air sourcesubstantially under the control of the fans of the rack-mountable itemsof electronic equipment. For example, when the cooling air source issupplied with air to be cooled from outside the data centre building,air from outside the data centre building is drawn into the cooling airsource substantially, such as substantially entirely, under the controlof the fans of the rack-mountable items of electronic equipment.Additionally or alternatively, when the cooling air source is suppliedwith air to be cooled from inside the data centre (for example, warm airreturning to the cooling air source from one or more rack mounted itemsof electronic equipment), the air from inside the data centre buildingis transported to the cooling air source substantially under the controlof the fans of the rack-mountable items of electronic equipment.

Preferably, the method comprises passing air through the cooling airsource substantially under the control of the fans of the rack-mountableitems of electronic equipment. Preferably, the cooling air sourcecomprises an adiabatic humidifier and the method comprises transportingair to be cooled to the adiabatic humidifier and transporting coolingair from the adiabatic humidifier substantially under the control of thefans of the rack-mountable items of electronic equipment. Preferably theadiabatic humidifier comprises a wetted matrix humidifier.

Preferably, the data centre building comprises an air extractioncorridor for receiving air from the one or more hot aisles, and themethod comprises transporting air from the one or more hot aisles to theair extraction corridor at least partially under the control of the fansof the rack-mountable items of electronic equipment. It may be that whenthe data centre comprises an air extraction corridor for receiving airfrom the one or more hot aisles the data centre building provides aparticularly low resistance, high volume air flow path for air that hasbeen used to cool the items of electronic equipment to be conveyed alongaway from the items of electronic equipment. Preferably, the airextraction corridor of the data centre building has a cross-sectionalarea of at least 3 m², preferably 5 m², for example 9 m², along 90% ofits length. It has been found that when the air extraction corridor hasa cross-sectional area of 3 m² or more along 90% of its length theresistance to air flow around the data centre building is reduced,thereby reducing the air velocity required to transport a given volumeof air that has been used to cool the items of electronic equipment awayfrom the from racks, thus also reducing the demand placed on the fans ofthe items of electronic equipment.

Optionally, the data centre comprises an adjustable exhaust vent forallowing air to pass from inside the data centre to outside the datacentre building. Preferably, the method comprises controlling theadjustable exhaust vent to vary the amount of air allowed to pass frominside the data centre to outside the data centre. Optionally, when thedata centre building comprises an air extraction corridor, the airextraction corridor comprises an adjustable exhaust vent for allowingair to be pass from inside the data centre to outside the data centrebuilding, and the method comprises controlling the adjustable exhaustvent to vary the amount of air allowed to pass from inside the datacentre to outside the data centre. It may be that when the methodcontrols the amount of hot air allowed to pass from inside the buildingto outside the building through the adjustable exhaust vent the methodefficiently balances the cooling air requirements of the electronicequipment to minimise the amount of mechanical cooling and/orhumidification/dehumidification required. It may be that the more hotair that is allowed to exit the data centre building, the more ambientair that is drawn into the data centre building. Thus, when the ambientair temperature is low, it may be desirable to allow more hot air toexit the building through the exhaust vent.

The one or more fans in the electronic equipment may be the primarymeans by which air is drawn into the cooling air source. For example,the one or more fans in the electronic equipment may be the primarymeans by which air is drawn in from outside the data centre, in the casewhere ambient air is used for cooling. It may be that the one or morefans in the electronic equipment are the primary means by which air isdrawn through the adiabatic cooler/evaporative humidifier when suchequipment forms part of the cooling air source. In certain embodimentsit may be possible for the one or more fans in the electronic equipmentto be the primary means by which air, exhausted from the items ofelectronic equipment, is moved further downstream, for example so as tobe (at least partially) exhausted out of the data centre (for example,to the atmosphere) and/or (at least partially) recirculated within thedata centre. In other embodiments there may be a need for further meansof encouraging air flows downstream of the items of electronicequipment. There may for example be one or more exhaust fans, forexample one or more variable speed fans, for assisting the expelling ofair out of the data centre building.

The above-mentioned exhaust vent may comprise a variable speed fan forexpelling air out of the data centre building. There may be a step ofcontrolling the speed of such a variable speed fan to adjust the amountof air expelled from the data centre building. It may be that the use ofan adjustable exhaust vent comprising a variable speed fan helps toprevent a build-up of hot air in the air extraction corridor, forexample when the data centre is operating in a mode in which the coolingair comprises mostly or entirely ambient air from outside the datacentre building. Alternatively or additionally, it may be that thevariable speed fan is used to assist in expelling hot air out of thedata centre building when outside conditions hinder such expulsion, forexample if the force of the wind outside opposes expulsion of hot airout of the data centre building. It will be appreciated that wind and/orother weather phenomena could lead to a build-up of air pressure on theoutside of the adjustable exhaust vent, preventing adequate expulsion ofhot air. It will be appreciated that, in the context of the presentinvention, the use of such exhaust fans (fans downstream of the items ofelectronic equipment that are operated to assist with the expelling ofair for example) does not assist, at least not in any significant way,with the drawing of cold air across the items of electronicequipment—such a step being performed substantially by means of the fansof the rack-mountable items of electronic equipment. It may be that themethod comprises operating the fans of the rack-mountable items ofelectronic equipment and the exhaust fans such that the sum aircirculation (in m³/s) caused by the rack-mountable items of electronicequipment is larger than the sum air circulation (in m³/s) caused by theexhaust fans. For example, the method comprises using the fans of therack-mounted items of electronic equipment to transport a larger volumeof air per second than the volume of air transported by the exhaustfans. This may be measured by operating the fans of the rack-mounteditems of electronic equipment but not the exhaust fans leaving all otherconditions the same and comparing the rate of air flow to when theexhaust fans, not the fans of the rack-mounted items of electronicequipment, are operating, leaving all other conditions the same. It maybe that the method comprises operating the data centre in a first modein which the exhaust fans are not used to assist in exhausting air outof the data centre, and a second mode in which the exhaust fans are usedto assist in exhausting air out of the data centre. Preferably, the datacentre is operated in the first mode for at least 25% of a given time(such as a month or a year), such as at least 50%, for example at least75% or at least 90%. Preferably, the method comprises using the exhaustfans to maintain a pre-determined pressure differential between the coldarea of the data centre and the hot area of the data centre. Forexample, it may be that the exhaust fans are only operated when thepressure differential between the cold and hot areas of the data centreexceeds a certain pre-set value. Preferably, the data centre isconfigured such that the fans of the items of electronic equipment arecapable of maintaining the pressure differential below the pre-set valuewithout the assistance of the exhaust fans for at least 25%, for exampleat least 50%, such as at least 75% or at least 90%, of the time that thedata centre operates.

Preferably, when the data centre building comprises an air extractioncorridor, the air extraction corridor comprises an adjustablerecirculation vent for allowing air to recirculate from the airextraction corridor to the cooling air source. The method may comprise astep of controlling the adjustable recirculation vent to vary the amountof air allowed to recirculate from the air extraction corridor to thecooling air source. It may be that when the method comprises controllingthe amount of hot air recirculated from the air extraction corridor backto the cooling air source, the method efficiently balances the coolingair requirements of the electronic equipment to minimise the amount ofmechanical cooling and/or humidification/ dehumidification required.

Preferably, the air extraction corridor has a cross-sectional area of atleast 3 m², for example 5 m², for its entire length from the one or morehot aisles to the adjustable exhaust vent and/or to the adjustablerecirculation vent.

Optionally, at least one of the one or more cold aisles comprises anadjustable vent for admitting cooling air into the cold aisle from theair supply corridor. Preferably, the method comprises controlling theadjustable vent to vary the amount of air supplied from the air supplycorridor to the one or more cold aisles.

Optionally, the one or more cold aisles comprises an adjustable venteddoor providing access to the air supply corridor, and the methodcomprises controlling the adjustable vented door to vary the amount ofair supplied from the air supply corridor to the one or more coldaisles. It may be that when the method comprises controlling the amountof air supplied from the air supply corridor to the one or more coldaisles the method efficiently regulates the supply of cooling air to theone or more cold aisles without unduly burdening the fans of the itemsof electronic equipment. For example, it may be that in a data centrecomprising two cold aisles, when the items of electronic equipment inthe first cold aisle are working at a higher load than the items ofelectronic equipment in the second cold aisle, more cooling air might berequired in the first cold aisle. Opening the vents of the adjustablevented door of the first cold aisle wider than those of the adjustablevented door of the second cold aisle may lower the air flow resistanceinto the first cold aisle thereby allowing the fans of the items ofelectronic equipment in the first cold aisle to draw in more cooling airwithout having to compete with the fans of items of electronic equipmentin the second cold aisle. The use of adjustable vented doors (such aslouvered doors, for example automatic louvered doors, under the controlof the data centre building control system) allows further control andmanagement of the cooling air supply to restrict/isolate the air flowpath away from areas where cooling air demand is lower, and to directcooling air to exactly where it is required.

It will be appreciated that the method of the first aspect of theinvention can be performed using a data centre having any one of a verylarge number of layout designs, providing of course that a lowresistance, high volume air flow path is provided from the cooling airsource to the racks of items of electronic equipment thereby allowinglow velocity, high volume distribution of cooling air. For example,using the air supply corridor and cold aisles as the principal air flowpath allows the velocity of the cooling air to be kept low, avoiding thecooling air unintentionally bypassing items of electronic equipmentlocated close to the point at which the cooling air enters the coldaisle.

The method of the first aspect of the invention helps avoid thehistorical server overheating problems associated with using air to coolservers and significantly raises the erroneously perceived threshold ofthe limits of air based server cooling. It will be appreciated thatelectronic equipment fan power typically constantly alters according todemand, maintaining the minimum flow of cooling air over the item ofelectronic equipment. It is preferred that each fan in the rack-mounteditems of electronic equipment is controlled by the corresponding item ofelectronic equipment to operate in one of two, possibly three andoptionally more levels of demand (“no demand” being included as such alevel) in dependence on the cooling needs of the item of electronicequipment (preferably as determined by the item of electronicequipment). Each fan may be thermostatically controlled, for example.The low resistance, high volume air flow path from the cooling airsource to the racks of items of electronic equipment allows the fans onthe items of electronic equipment to draw sufficient cooling air tomaintain adequate cooling of all items.

It may be that one or more of the items of electronic equipment areservers, for example server blades. It may be that one or more of theitems of electronic equipment comprises a plurality of fans. It may bethat one or more of the items of electronic equipment are networkequipment. It may be that one or more of the items of electronicequipment are in the form of operational IT equipment being items ofequipment that process, retrieve and/or store computer data, such asclient data—i.e. the core IT equipment that provides the function of thedata centre.

The method may be so performed that the air flow rate at any positionalong the (upstream) air flow path is less than 110% of the sum of theair flow rates effected by the fans of all those items of electronicequipment supplied with air from that position. It may be that there aresome positions along the (upstream) air flow path at which the air flowrate is less than the sum of the air flow rates effected by the fans ofall those items of electronic equipment supplied with air from thatposition (as a result for example in losses through air resistance andthe like). The method may be so performed that the air flow rate at anyposition along the (upstream) air flow path is more than 50% of the sumof the air flow rates effected by the fans of all those items ofelectronic equipment supplied with air from that position. Attainingsuch a relatively high flow rate at all positions on the flow pathupstream of the racks may be achievable my means of providing a highcross-sectional area and low resistance air flow path.

According to a second aspect of the invention, the invention provides adata centre building for use in the method of the first aspect of theinvention. The data centre building of the second aspect of theinvention may thus comprise a cooling air source. The data centrebuilding may comprise at least one rack room having a floor and aplurality of rack storage areas on the floor, each rack storage areabeing arranged to accommodate a plurality of racks in which a pluralityof rack-mountable electronic components having at least one fan may behoused. The data centre building may comprise one or more such racksinstalled in the building. Such racks may include one or more electroniccomponents mounted therein. There may be one or more cold aisles, forexample in a given rack room. There may be only one discernible rackroom in the data centre, or there may be more than one. There may be oneor more hot aisles. The data centre building may comprise an air supplycorridor for transporting cooling air, above the floor, from the coolingair source to the one or more cold aisles. In embodiments of theinvention, the data centre building is arranged such that, in use,transport of the cooling air from the cooling air source to the racks inwhich the items of electronic equipment are mounted (which may requiretransporting of the cooling air from the cooling air source to one ormore cold aisles) is controlled and/or effected substantially entirelyby the fans of the rack-mounted electronic components. When the datacentre is arranged in this manner, the data centre may be operatedparticularly efficiently.

Preferably, the data centre is arranged such that the transport of thecooling air is controlled and/or effected entirely by the fans of therack-mountable electronic components. Such an arrangement may allow fora particularly efficient operation of the data centre.

Optionally, the air supply corridor has a cross-sectional area of atleast 3 m², for example 5 m², such as 9 m², for at least 90% of itslength. Such an air supply corridor provides a particularly lowresistance to air flow.

Preferably, the data centre building comprises an adjustable intake ventfor admitting ambient air from outside the data centre building into thedata centre building.

Optionally, the data centre building comprises a heat exchanger forexchanging the heat from warm air inside the data centre with cooler airoutside of the data centre.

Preferably, the cooling air source comprises an adiabatic humidifier.

Optionally, the data centre comprises one or more hot corridors forreceiving air from the one or more hot aisles. Optionally, the one ormore hot corridors comprises an adjustable exhaust vent for exhaustinghot air out of the data centre building. Preferably, the adjustableexhaust vent comprises a fan for expelling air out of the data centrebuilding. Optionally, the one or more hot corridors comprises anadjustable recirculation vent for allowing hot air to recirculate to thecooling air source.

Preferably, the data centre comprises an internal air flow path definedby the cooling air source, the one or more cold corridors, the one ormore cold aisles, the rack storage areas holding a plurality ofelectronic components in the form of servers having at least oneintegral fan, the one or more hot aisles and the one or more hotcorridors, wherein the internal air flow path is free from aircirculation devices such as fans, other than the integral fans of theservers. It will be appreciated that an integral fan of a server is afan that is provided to meet the cooling requirements of that individualserver. Preferably, the internal air flow path is an isolated air flowpath, meaning that the air flow path is arranged such that during normaloperation, little or no air circulating along the path exits the datacentre building and little or no air from outside the data centrebuilding is admitted into the air flow path. In such an isolated airflow path arrangement, it may be that the data centre comprises anindirect air handling unit as the cooling air source, such as an airhandling unit comprising a heat exchanger, for transferring heat fromthe air circulating along the isolated air flow path to ambient airoutside of the data centre. Preferably, when the internal air flow pathis an isolated air flow path, the internal air flow path is free fromair purifying devices such as filters or filter banks, thus reducing theresistance to air flow along the internal air flow path. Preferably, theinternal air flow path extends from a first location in the data centreupstream of the cooling air source to a second location in the datacentre downstream of the electronic components.

It will of course be appreciated that features described in relation toone aspect of the present invention may be incorporated into the otheraspect of the present invention. For example, the apparatus of theinvention may incorporate any of the features described with referenceto the method of the invention and vice versa.

DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying schematic drawings ofwhich:

FIG. 1 shows a prior art rack room;

FIG. 2 shows a schematic diagram of the method of the first aspect ofthe invention;

FIG. 3 shows a plan view of a data centre for use in a method accordingto an embodiment of the invention;

FIG. 4 shows a plan view of a data centre for use in a method accordingto another embodiment of the invention;

FIG. 5 shows a cross-sectional view of a data centre for use in a methodaccording to another embodiment of the invention;

FIG. 6 shows a cross-sectional view of a data centre for use in a methodaccording to another embodiment of the invention;

FIG. 7 shows a plan view of a data centre for use in a method accordingto another embodiment of the invention;

FIG. 8 shows a plan view of a data centre for use in a method accordingto another embodiment of the invention;

FIG. 9 shows a plan view of a data centre for use in a method accordingto another embodiment of the invention;

FIG. 10 shows a cross-sectional view of a data centre for use in amethod according to another embodiment of the invention;

FIG. 11 shows a plan view of a data centre for use in a method accordingto another embodiment of the invention;

FIG. 12 shows a plan view of a data centre for use in a method accordingto another embodiment of the invention;

FIG. 13 shows a plan view of a data centre for use in a method accordingto another embodiment of the invention;

FIG. 14 shows a plan view of a data centre for use in a method accordingto another embodiment of the invention; and

FIG. 15 shows a cross-sectional view of a data centre for use in amethod according to another embodiment of the invention.

DETAILED DESCRIPTION

FIG. 2 shows a schematic of a method of cooling a data centre accordingto a first embodiment of the invention. The data centre comprises acooling air source 201, a rack room 202 having a floor and a pluralityof rack storage areas 203 a-203 d on the floor, each rack storage areaaccommodating a plurality of racks in which a plurality ofrack-mountable items of electronic equipment having at least one fan 204are housed; a cold aisle 205 in the rack room 202; a hot aisle 206 inthe rack room 202; and an air supply corridor 207 for transportingcooling air 208, above the floor, from the cooling air source 201 to thecold aisle 205. The method of the first embodiment of the inventioncomprises transporting cooling air from the cooling air source 201 tothe cold aisle 205 substantially under the control of the fans 204 ofthe rack-mountable items of electronic equipment. The method alsocomprises returning heated air 209 from the hot aisle 206 to the coolingair source 201 via an air extraction corridor 210, optionally expellinghot air 211 from the data centre building and optionally drawing inambient air 212 into the cooling air source 201.

Key principles of the method of the first embodiment of the inventionare:

1. The air conditioning arrangement (cooling air source 201) has nofans. It may contain, according to specific or climatic requirements, afiltration bank, evaporative or mechanical cooling, bypasses and meansof control and may be in fluid communication with the externalenvironment or indirectly in contact with it through the use of a heatexchange system.

2. The air conditioning arrangement is in fluid communication with acold rack space in which the front face of the server racks is located.

3. The rear of the server racks is located in a separated hot space orspaces, the racks forming part of the separation between the hot andcold spaces. Any server ‘u’ spaces or rack spaces that are not used areblanked to ensure that air can only entrain from the hot to cold spacesvia the servers.

4. All air movement through the system is generated by the individualserver fans.

5. Activation of the various air conditioning components and entrainmentcomponents is managed by a control system based on information inputfrom sensors used in the control configuration.

6. Optional automatic louvre doors can be used in strategic positions tobalance individual cold spaces with high and low air demands if thedesign requires. The door would be open more for space with highaggregate demand and ‘throttle back’ for a low demand space.

7. An additional small extract fan may be used in the hot space todissipate pressure build up in some conditions.

FIG. 3 shows a plan view of a data centre 301 for use in a methodaccording to an embodiment of the invention. The data centre 301comprises an enclosed hot/cold space configuration. The plan shows thatwhen the data centre 300 is used in the method of a second embodiment ofthe invention, ambient air 301 is drawn in from the outside the datacentre 300 through adjustable intake louvres 302 the air conditioningarrangement 303 (where it is conditioned to the control set points) bythe server fans 304. Conditioned air 305 enters cold space 306 and thencold rack spaces 307 where the conditioned air 305 is drawn through eachserver 308 individually by the integral server fans 304. Hot air 309 isexhausted by each individual server 308 into a hot space 310. Hot air309 is allowed to exit the building 300 through adjustable exhaustlouvres 311 (to the extent that the hot air 309 is not required forrecirculation), and/or allowed to pass through adjustable return louvres312 into a mixing space 313 (to the extent that hot air is required forrecirculation to the air conditioning arrangement 303). The cold space306 is separated from the cold rack spaces 307 by means of doors 314having adjustable vents for controlling the flow of conditioned air 305into the cold rack space 307. In the method of this embodiment of theinvention, the adjustable vents of the doors 314 may be used to limitthe amount of conditioned air 305 that can be drawn into a particularcold rack space 307 thus favouring flow of conditioned air 305 to one ormore other cold rack spaces 307 that have a greater demand forconditioned air 305. In this way, the method of this embodiment of theinvention may vary the air flow resistance of different air flow pathsthrough the data centre to improve efficiency of the method. The Airflow through the hot space 310 is controlled by the aggregate power ofthe server fans. The data centre 300 also comprises exhaust fan 315 foraiding the exhaust of hot air 309 out of the hot space 310. Dependingon, for example, the weather conditions outside of the data centre, theexhaust fan 3015 may be operated to avoid a build-up in air pressure inthe hot space 310, which may otherwise inhibit air circulation by theserver fans 304.

The hot air 309 may be mixed with ambient air 301 from outside the datacentre building 300 in the mixing space 313 when the method of thisembodiment of the invention is operating in partial recirculation mode(adjustable intake louvres 302, adjustable exhaust louvres 311 andadjustable return louvres 312 all being at least partially open). Whenthe method of this embodiment of the invention is operating in fullexhaust mode (also referred to as full ambient air cooling mode),substantially all or all of the hot air 309 is exhausted through theadjustable exhaust louvres 311, and the air conditioning arrangement 303is supplied substantially entirely or entirely with ambient air 301 fromoutside the data centre building 300 (adjustable intake louvres 302 andadjustable exhaust louvres 311 being open and adjustable return louvres312 being open). When the method of this embodiment of the invention isoperating in full recirculation mode, substantially all or all of thehot air 309 is returned to the air conditioning arrangement 303, andsubstantially no or no ambient air 301 from outside the data centrebuilding is supplied to the air conditioning arrangement 303 (adjustableintake louvres 302 and adjustable exhaust louvres 311 being closed andadjustable return louvres 312 being open). It will be appreciated thatin operating a data centre according to the method of this embodiment ofthe invention, the method may comprise varying the mode of operationfrom full recirculation to partial recirculation to full ambient coolingdepending on the condition of the ambient air and on the loadexperienced by the items of electronic equipment.

FIG. 4 shows a plan view of a data centre 400 for use in a methodaccording to a third embodiment of the invention, in which the coolingair source utilises a heat exchanger 401. The depiction of the heatexchange unit is purely figurative. A direct expansion (DX) cooling unit402 is provided downstream of the heat exchanger 401. Those parts ofFIG. 4 having the same meaning as in FIG. 3 are labelled with the samereference numerals. The data centre 400 for use in the method of thethird embodiment of the invention is a closed system, and so does notinclude exhaust or intake louvres.

FIG. 5 shows a cross-sectional view of a data centre 500 for use in amethod according to a fourth embodiment of the invention. In the datacentre shown, the hot space 510 is in the form of an overhead plenum.Those parts of FIG. 5 having the same meaning as in FIG. 3 are labelledwith the same reference numerals.

FIG. 6 shows a cross-sectional view of a data centre 600 for use in amethod according to a fifth embodiment of the invention. In the datacentre shown, the air conditioning arrangement 303 is positioned abovethe cold space 306. Those parts of FIG. 6 having the same meaning as inFIG. 3 are labelled with the same reference numerals.

FIG. 7 shows a plan view of a data centre 700 for use in a methodaccording to a sixth embodiment of the invention. The figure shows how,in a sixth embodiment of the invention, the method can be used in a datacentre created from an existing internal space, in this case in anexisting office building. Those parts of FIG. 7 having the same meaningas in FIG. 3 are labelled with the same reference numerals.

FIG. 8 shows a plan view of a data centre 800 for use in a methodaccording to a seventh embodiment of the invention. The data centre isprovided with a filter bank 801 upstream of the air conditioning unit,allowing the return louvres 312 between the hot space 310 and the mixingspace 313 to be positioned between the filter 801 and the airconditioning arrangement 303, thereby decreasing resistance from thefilters when the method of the embodiment utilises air recirculation.Those parts of FIG. 8 having the same meaning as in FIG. 3 are labelledwith the same reference numerals.

FIG. 9 shows a plan view of a data centre 900 for use in a methodaccording to an eighth embodiment of the invention. In the data centreshown, the air conditioning arrangement 303 is positioned in the middleof the data centre. Those parts of FIG. 9 having the same meaning as inFIG. 3 are labelled with the same reference numerals.

FIG. 10 shows a cross-sectional view of a data centre 1000 for use in amethod according to a ninth embodiment of the invention. In the datacentre shown, the air conditioning arrangement 303 is sited on an upperstorey 1001, and the rack space is sited on the lower storey 1002 undera hot space plenum 1003 which acts as a route for hot air 309 to beeither recirculated or exhausted. Cut outs are provided to allowconditioned air 305 to pass through the hot plenum 1003 level to thecold space 306. Those parts of FIG. 10 having the same meaning as inFIG. 3 are labelled with the same reference numerals.

FIG. 11 shows a plan view of a data centre 1100 for use in a methodaccording to a tenth embodiment of the invention. Those parts of FIG. 11having the same meaning as in FIG. 3 are labelled with the samereference numerals.

FIG. 12 shows a plan view of a data centre 1200 for use in a methodaccording to an eleventh embodiment of the invention. Those parts ofFIG. 12 having the same meaning as in FIG. 3 are labelled with the samereference numerals.

FIG. 13 shows a plan view of a data centre 1300 for use in a methodaccording to a twelfth embodiment of the invention. In the data centreshown, the data centre is divided into three data hall spaces, two ofwhich share a hot space 1301 for exhaust and recirculation. Those partsof FIG. 13 having the same meaning as in FIG. 3 are labelled with thesame reference numerals.

FIG. 14 shows a plan view of a data centre 1400 for use in a methodaccording to a thirteenth embodiment of the invention. In the datacentre shown, multiple air conditioning arrangements 303 are disposed tofeed one common cold space 1401, and groups of racks share a hot space‘chimney’ 1402 which connects to a shared overhead hot plenum 1403 forrecirculation (with optional mechanical assistance 1404 to direct thewarm air back down to the mixing space 313) or exhaust. Those parts ofFIG. 14 having the same meaning as in FIG. 3 are labelled with the samereference numerals.

FIG. 15 shows a cross-sectional view of the data centre 1400 of FIG. 14taken along the line X-X indicated by the black dotted arrows in FIG.14. Those parts of FIG. 15 having the same meaning as in FIG. 3 arelabelled with the same reference numerals.

Whilst the present invention has been described and illustrated withreference to particular embodiments, it will be appreciated by those ofordinary skill in the art that the invention lends itself to manydifferent variations not specifically illustrated herein.

Where in the foregoing description, integers or elements are mentionedwhich have known, obvious or foreseeable equivalents, then suchequivalents are herein incorporated as if individually set forth.Reference should be made to the claims for determining the true scope ofthe present invention, which should be construed so as to encompass anysuch equivalents. It will also be appreciated by the reader thatintegers or features of the invention that are described as preferable,advantageous, convenient or the like are optional and do not limit thescope of the independent claims. Moreover, it is to be understood thatsuch optional integers or features, whilst of possible benefit in someembodiments of the invention, may not be desirable, and may therefore beabsent, in other embodiments.

1-13. (canceled)
 14. A method of cooling servers in a data centre,wherein the data centre has a cooling air source, a cold area and a hotarea, the cooling air source having a heat exchanger for exchanging heatbetween an internal air flow path segregated from an external air flowpath, the external air flow path being in fluid communication withambient air outside the data centre, the servers having integral serverfans, and the data centre having a closed air circuit configured forcirculation of air from the cold area into the hot area via the servers,and from the hot area back into the cold area via the internal air flowpath of the cooling air source, wherein the method is performed byoperating the integral server fans to collectively cause circulation ofair around the closed air circuit without assistance of another airmover.
 15. The method of claim 14, wherein the cold area comprises anair supply corridor and a plurality of cold aisles, and wherein theclosed air circuit is configured so that air circulates through the coldarea by passing from the air supply corridor into the plurality of coldaisles, optionally wherein the hot area comprises a plurality of hotaisles and an air extraction corridor, and wherein the closed aircircuit is configured so that air circulates through the hot area bypassing from the plurality of hot aisles into the air extractioncorridor.
 16. The method of claim 15, wherein the closed air circuit isconfigured so that air circulates directly from the internal air flowpath of the cooling air source into the air supply corridor, optionallywherein the closed air circuit is configured so that air circulatesdirectly from the air extraction corridor into the internal air flowpath of the cooling air source.
 17. The method of claim 15, wherein theair supply corridor is a personnel corridor configured to providepersonnel access to the cold aisles, optionally wherein the airextraction corridor is a personnel corridor configured to providepersonnel access to the hot aisles.
 18. The method of claim 14, whereinthe cooling air source comprises an adiabatic humidifier, and whereinthe method comprises operating the adiabatic cooler to control thehumidity and/or temperature of air in the external air flow path. 19.The method of claim 15, wherein each of the plurality of cold aislescomprises an adjustable vented door providing access to the air supplycorridor, and wherein the method comprises controlling each adjustablevented door to vary the amount of air circulated from the air supplycorridor into each cold aisle.
 20. The method of claim 14, wherein thedata centre comprises an air refreshing system, and wherein the methodcomprises operating the air refreshing system to admit fresh air intothe data centre from outside the data centre.
 21. A data centre, whereinthe data centre has a cooling air source, a cold area and a hot area,the cooling air source having a heat exchanger for exchanging heatbetween an internal air flow path segregated from an external air flowpath, the external air flow path being in fluid communication withambient air outside the data centre, the servers having integral serverfans, and the data centre having a closed air circuit configured forcirculation of air from the cold area into the hot area via the servers,and from the hot area back into the cold area via the internal air flowpath of the cooling air source, wherein the data centre and the integralserver fans are configured so that the integral server fans aresufficient to collectively cause circulation of air around the closedair circuit without assistance of another air mover.
 22. The data centreof claim 21, wherein the cold area comprises an air supply corridor anda plurality of cold aisles, and wherein the closed air circuit isconfigured so that air circulates through the cold area by passing fromthe air supply corridor into the plurality of cold aisles, optionallywherein the hot area comprises a plurality of hot aisles and an airextraction corridor, and wherein the closed air circuit is configured sothat air circulates through the hot area by passing from the pluralityof hot aisles into the air extraction corridor.
 23. The data centre ofclaim 22, wherein the closed air circuit is configured so that aircirculates directly from the internal air flow path of the cooling airsource into the air supply corridor, optionally wherein the closed aircircuit is configured so that air circulates directly from the airextraction corridor into the internal air flow path of the cooling airsource.
 24. The data centre of claim 22, wherein the air supply corridoris a personnel corridor configured to provide personnel access to thecold aisles, optionally wherein the air extraction corridor is apersonnel corridor configured to provide personnel access to the hotaisles.
 25. The data centre of claim 21, wherein the cooling air sourcecomprises an adiabatic humidifier operable to control the humidityand/or temperature of air in the external air flow path.
 26. The datacentre of claim 22, wherein each of the plurality of cold aislescomprises an adjustable vented door providing access to the air supplycorridor and controllable to vary the amount of air circulated from theair supply corridor into each cold aisle.
 27. The data centre of claim21, wherein the data centre comprises an air refreshing system foradmitting fresh air into the data centre from outside the data centre.28. A method of cooling servers in a data centre, wherein the datacentre comprises: servers arranged in the data centre in rows separatingalternating cold aisles and hot aisles, a first personnel corridor influid communication with the cold aisles, and an indirect air handlingunit configured to receive warm air from the servers via the hot aislesand to provide cool air to the servers via the first personnel corridorand the cold aisles, wherein the first personnel corridor is separate tothe cold aisles and located on the same level of the data centre as thecold aisles, and wherein the servers comprise server fans; wherein themethod is performed by: operating the indirect air handling unit to coolthe warm air by exchanging heat with air outside the data centre therebyproducing the cool air, and operating the server fans to draw in coolair from the cold aisles, transport the cool air through the serversthereby producing the warm air, and to exhaust the warm air into the hotaisles, wherein said operation of the server fans is sufficient todirectly cause circulation of the cooling air along the first personnelcorridor and along the cold aisles from the indirect air handling unitto the servers, cause circulation of the warm air along the hot aislesfrom the servers to the indirect air handling unit, and causecirculation of air through the indirect air handling unit.
 29. Themethod of claim 28, wherein the data centre comprises a second personnelcorridor in fluid communication with the hot aisles, wherein theindirect air handling unit is configured to receive warm air from theservers via the second personnel corridor and the hot aisles, whereinthe second personnel corridor is separate to the hot aisles and locatedon the same level of the data centre as the hot aisles, and whereinoperating the server fans is sufficient to cause circulation of the warmair along the hot aisles and along the second personnel corridor fromthe servers to the indirect air handling unit.
 30. The method of claim28, wherein the indirect air handling unit is located on the same levelof the data centre as the cold aisles and the first personnel corridor.31. The method of claim 29, wherein the data centre defines a continuousairflow path extending through the indirect air handling unit, from theair handling unit to the servers via the first personnel corridor andthe cold aisles, and from the servers to the indirect air handling unitvia the hot aisles and the second personnel corridor, and wherein thecontinuous airflow path is horizontal.
 32. The method of claim 28,wherein the indirect air handling unit comprises an adiabatichumidifier, and wherein the method comprises operating the adiabaticcooler to control the humidity and/or temperature of outside air fromoutside the data centre before said outside air is used for heatexchange with air inside the data centre.
 33. The method of claim 28,wherein each of the cold aisles comprises an adjustable vented doorproviding access to the first personnel corridor, and wherein the methodcomprises controlling each adjustable vented door to vary the amount ofair circulated from the first personnel corridor into each cold aisle.34. The method of claim 28, wherein the data centre comprises an airrefreshing system, and wherein the method comprises operating the airrefreshing system to admit fresh air into the data centre from outsidethe data centre.
 35. A data centre, wherein the data centre comprises:servers arranged in the data centre in rows separating alternating coldaisles and hot aisles, a first personnel corridor in fluid communicationwith the cold aisles, and an indirect air handling unit configured toreceive warm air from the servers via the hot aisles and to provide coolair to the servers via the first personnel corridor and the cold aisles,wherein the first personnel corridor is separate to the cold aisles andlocated on the same level of the data centre as the cold aisles, andwherein the servers comprise server fans; wherein the indirect airhandling unit is operable to cool the warm air by exchanging heat withair outside the data centre in order to produce said cool air, whereinthe server fans are operable to draw in cool air from the cold aisles,transport the cool air through the servers thereby producing the warmair, and to exhaust the warm air into the hot aisles, and wherein thedata centre is configured so that said operation of the server fans issufficient to directly cause circulation of the cooling air along thefirst personnel corridor and along the cold aisles from the indirect airhandling unit to the servers, cause circulation of the warm air alongthe hot aisles from the servers to the indirect air handling unit, andcause circulation of air through the indirect air handling unit.
 36. Thedata centre of claim 35, wherein the data centre comprises a secondpersonnel corridor in fluid communication with the hot aisles, whereinthe indirect air handling unit is configured to receive warm air fromthe servers via the second personnel corridor and the hot aisles,wherein the second personnel corridor is separate to the hot aisles andlocated on the same level of the data centre as the hot aisles, andwherein the data centre is configured so that said operation of theserver fans is sufficient to directly cause circulation of the warm airalong the hot aisles and along the second personnel corridor from theservers to the indirect air handling unit.
 37. The data centre of claim35, wherein the indirect air handling unit is located on the same levelof the data centre as the cold aisles and the first personnel corridor.38. The data centre of claim 36, wherein the data centre defines acontinuous airflow path extending through the indirect air handlingunit, from the air handling unit to the servers via the first personnelcorridor and the cold aisles, and from the servers to the indirect airhandling unit via the hot aisles and the second personnel corridor, andwherein the continuous airflow path is horizontal.
 39. The data centreof claim 35, wherein the indirect air handling unit comprises anadiabatic humidifier operable to control the humidity and/or temperatureof outside air from outside the data centre before said outside air isused for heat exchange with air inside the data centre.
 40. The datacentre of claim 35, wherein each of the cold aisles comprises anadjustable vented door configured to provide access to the firstpersonnel corridor, and controllable to vary the amount of aircirculated from the first personnel corridor into each cold aisle. 41.The data centre of claim 35, wherein the data centre comprises an airrefreshing system operable to admit fresh air into the data centre fromoutside the data centre.